JP2024150776A - Implantable medical device for stimulating the human or animal heart - Google Patents

Abstract

An implantable medical device for stimulating the heart of a human or animal is provided, the implantable medical device comprising a control unit, a storage unit, a stimulation unit, and a detection unit for detecting electrical signals of the same heart, the storage unit including a computer readable program for causing the control unit to execute the steps of: a) detecting a capture threshold during an observation period with the detection unit, where each capture threshold is detected in response to a pacing pulse delivered by the stimulation unit (step 210), b) storing the detected capture thresholds in the storage unit, and c) decreasing each day the voltage U of the pacing output of the stimulation unit by at most a predetermined maximum value, where the voltage U of the pacing output remains at least as high as the determined maximum capture threshold within a period equal to or shorter than the observation period (step 230, 240).

Description

The present invention relates to an implantable medical device as described in the preamble of claim 1, a method for controlling the operation of such an implantable medical device as described in the preamble of claim 10, a computer program product as described in the preamble of claim 11, and another implantable medical device as described in the preamble of claim 13.

Implantable medical devices for stimulating the human or animal heart, such as cardiac pacemakers, typically use a capture control function to assess ventricular capture. Capture can be described as successful ventricular stimulation, i.e., it is defined as ventricular cardiac activity in response to an external or artificial stimulus (e.g., by a pacemaker).

Capture control typically uses an algorithm to calculate the pacing output necessary to reliably achieve capture while limiting the pacing output to minimize power consumption by the implantable medical device. The capture control periodically measures the capture threshold and automatically adjusts the pacing output using the following basic calculation: previous threshold + safety margin = pacing output.

Often, capture control is performed once a day and the applied pacing output is reduced during the capture test to determine the capture threshold. Starting with a pacing output having a high amplitude, the amplitude of the pacing output is iteratively reduced to determine the lowest amplitude that can still capture ventricular activity.

Traditional safety margin algorithms add a fixed margin to either the last measured threshold or the maximum threshold over the time period under evaluation. These methods typically result in relatively high pacing outputs and therefore require relatively high power consumption.

WO2017/139197A1 describes a capture management method that calculates the difference between the minimum and maximum thresholds of a number of last determined thresholds in a rolling time window. The higher the determined difference, the higher the safety margin that is added to the determined capture threshold to determine the pacing output to be used. Thus, the method utilizes a variable safety margin that is added to the highest capture threshold determined in a rolling time window, with a high margin if the variance of the determined capture thresholds is large and a low safety margin if the variance of the determined capture thresholds is small.

US2014/0350623A1 describes a method for identifying candidate pulse widths corresponding to the lowest pulse energy sufficient to achieve capture in the patient's cardiac tissue. In this context, the application of different safety margins is also described.

U.S. Patent Application Publication No. 2016/0346552 (A1) and U.S. Patent Application Publication No. 2018/0036547 (A1) illustratively describe the application of threshold tests and safety margins to a determined capture threshold to determine the pacing output (stimulation amplitude).

The object of the present invention is to provide an implantable medical device for stimulating the human or animal heart, which consumes less power than implantable devices known from the prior art, but still ensures high safety for the patient with regard to cardiac capture.

This object is achieved by an implantable medical device having the features of claim 1. Such an implantable medical device is intended to stimulate the human or animal heart. It comprises a control unit, a memory unit, a stimulation unit for stimulating a cardiac area of the human or animal heart and a detection unit for detecting electrical signals of the same heart. In this context, the detection unit typically detects ventricular signals of the heart. The stimulation unit can stimulate the atria or ventricles of the human or animal heart. Often, the stimulation unit is intended to stimulate the right ventricle of the patient's heart.

In accordance with the presently claimed invention, the storage unit contains a computer readable program that, when executed on the control unit, causes the control unit to perform the steps described below.

In a first step, the capture threshold is detected by means of the detection unit. This detection is performed during an observation period. In this context, each capture threshold is detected in response to a sequence of pacing pulses delivered by the stimulation unit. Thus, the detection unit detects cardiac activity in response to an external or artificial stimulus.

The detected capture threshold is stored in a storage unit. Typically, time information is stored along with the capture threshold. Then, the time at which a particular capture threshold was detected can be easily seen.

A threshold difference is determined between each pair of two consecutive capture thresholds. For such a determination, at least two capture thresholds are required. If a first capture threshold and a second capture threshold are detected, a threshold-to-threshold difference between the first and second capture thresholds can be calculated. If a third capture threshold is then determined, a threshold-to-threshold difference between the second and third capture thresholds can be calculated. As an example, for a capture threshold of 30, a threshold-to-threshold difference of 29 occurs between two consecutive capture thresholds in each case.

The calculated inter-threshold difference is then further evaluated. For this purpose, the maximum inter-threshold difference determined within the observation period is identified. If this maximum inter-threshold difference is equal to or greater than a predefined limit value, this indicates that the inter-threshold variety is rather large. A higher pacing output is then required to safely guarantee ventricular capture. The pacing output of the stimulation unit is therefore adjusted in this option based on the maximum capture threshold determined within the first period. In this context, the first period is equal to or less than the observation period.

On the other hand, if the difference between the maximum determined thresholds within the observation period is smaller than a predefined limit value, this indicates that the variation between the thresholds of the individual thresholds is relatively small. It is then possible to ensure that cardiac capture is achieved by only relying on the maximum amplitude in a period shorter than the first period. The pacing output of the stimulation unit is therefore adjusted in this option based on the maximum capture threshold determined in a second period, the second period being shorter than the first period.

It should be appreciated that the first and second time periods span from the time of adjusting the pacing output of the stimulation unit to the past. In this manner, the first time period covers more capture thresholds and therefore more inter-threshold differences than the second time period, and both the first and second time periods cover the most recent inter-threshold differences prior to the adjustment of the pacing output of the stimulation unit.

This dynamic aspect of the algorithm used by the computer readable program provides a power saving opportunity that considers the power and safety tradeoff with the length of the maximum threshold evaluation period, i.e., the first or second period. By lengthening the evaluation period that tracks the maximum measured capture threshold, a large increase in the overall average pace output amplitude exists. However, the dynamic performance reduces the overall average pace output amplitude during the period when the capture threshold is stable by shortening this maximum capture threshold evaluation period to the second period.

The first and second periods are rolling window periods that always end at a time when the pacing output of the stimulation unit is adjusted by the method used by the computer readable program. Thus, the end of the period always moves forward in time. Similarly, if the period itself is not extended, the start of each period also moves forward in time. Thus, the presently claimed implantable medical device is one that supports capture thresholding including storage of capture thresholds using a rolling window, maximum threshold measurement, and inter-threshold variation measurement.

In one embodiment, the implantable medical device is an intracardiac device. The device is capable of delivering stimuli to cardiac tissue and measuring the capture threshold for cardiac capture or ventricular capture, respectively.

In contrast to prior art solutions, the method used by the presently claimed implantable medical device uses a new measure of threshold stability to determine how the length of the capture threshold evaluation period should be tracked to measure the patient's maximum capture threshold and determine pacing output based on this maximum capture threshold. This allows for a faster dynamic response during periods of stable capture threshold that reduces overall pacing output, while maintaining safety through a longer window during periods of capture threshold instability.

In one embodiment, the progress of the capture threshold is evaluated. In this embodiment, the stored capture threshold is used, for example, to evaluate whether there is a risk of undesired detachment of the implantable medical device from the cardiac tissue. If a continuous increase in the capture threshold is detected, this may indicate that the implantable medical device is about to detach from the cardiac tissue. In such a case, immediate counteraction can be taken to ensure safe implantation of the implantable medical device at the intended implantation site. Thus, in this embodiment, patient safety is improved. If the capture threshold first increases, then decreases and then increases and decreases again, this can be seen as an indication that there is no detachment of the implantable medical device from its implantation site, but rather reflects a natural variation of the capture threshold.

In one embodiment, the step of detecting the capture threshold using the detection unit is performed once a day. For this purpose, typically several measurements are required during which the pacing output used to stimulate the cardiac tissue is repeatedly lowered. The capture threshold is the last value of the pacing output at which capture can be determined, and the first pacing output below the capture threshold at which cardiac capture cannot be detected.

In one embodiment, the computer readable program causes the control unit to determine the pacing output by adding a safety margin to the maximum capture threshold, and the pacing output is adjusted based on the maximum capture threshold. Such a safety margin ensures cardiac capture even in the presence of other small variations in the capture threshold. Thus, such a safety margin improves patient safety, even if it consumes somewhat more energy than working without the safety margin. In other words, the safety margin reliably guarantees that cardiac capture will occur due to stimulation with a pacing output resulting from adding the safety margin to a predetermined maximum capture threshold for the first or second period.

In one embodiment, the computer readable program causes the control unit to set the safety margin independent of the determined inter-threshold difference and/or independent of the determined maximum capture threshold. Thus, in contrast to prior art solutions that rely on variation of the safety margin applied to a particular maximum capture threshold to determine the final pacing output, this embodiment of the presently claimed invention does not vary the safety margin but rather relies on skilled selection of the maximum threshold applied to calculate the pacing output. As already outlined, the presently claimed approach better reflects the physiological needs of the patient, whose heart is stimulated by the implantable medical device, while at the same time saving a significant amount of the energy required to pace the patient's heart. The approach taken by the presently described invention does not require a variable safety margin. Rather, the safety margin can be kept constant over the entire life of the implantable medical device, or at least nearly the entire life of the implantable medical device.

In one embodiment, the computer readable program causes the control unit to set the safety margin during the third period of time higher than after the third period of time. In this context, the third period of time is the period immediately following implantation of the implantable medical device. This embodiment takes into account that the capture threshold is typically somewhat higher and more variable during the first week after implantation, and then typically decreases to a lower, relatively constant value. Thus, combining the previous embodiment with this embodiment with each other, the safety margin changes only during the very first time after implantation, and remains constant for the remaining life of the implantable medical device. This can be considered as a constant safety margin for substantially the entire life of the implantable medical device. In one embodiment, the term "substantially the entire life of the implantable medical device" should be interpreted to mean the entire life minus the third period of time (regardless of any variation in the safety margin within the third period of time).

In one embodiment, the third period of time is a period of time ranging from 1 to 200 days, in particular from 5 to 190 days, in particular from 10 to 180 days, in particular from 20 to 170 days, in particular from 30 to 160 days, in particular from 40 to 150 days, in particular from 50 to 140 days, in particular from 60 to 130 days, in particular from 70 to 120 days, in particular from 80 to 110 days, in particular from 90 to 100 days. In any case, the third period of time begins immediately following implantation of the implantable medical device, in particular implantation of the implantable medical device into the patient's heart.

In one embodiment, the implantable medical device is a leadless pacemaker. Leadless pacemakers are implanted in a patient's heart; i.e., they can also be referred to as intracardiac devices. Leadless pacemakers are typically smaller than conventional pacemakers, thus requiring less space for an energy source such as a battery. Thus, the power consumption of a leadless pacemaker can be controlled much better than that of conventional pacemakers. Thus, leadless pacemakers are a very interesting field of application of the presently claimed invention, as it can significantly extend the lifetime of leadless pacemakers, thus making such devices even more attractive than those already in use.

In one embodiment, the computer readable program causes the control unit to reduce the voltage of the pacing output by at most a predetermined maximum value each day. When this embodiment is applied, the initial voltage of the pacing output is limited to more than the potentially possible range depending on the determined capture threshold and the interthreshold difference. Thus, operation of the implantable medical device according to this embodiment results in a higher energy consumption than absolutely necessary. However, it also increases the safety of the patient. Furthermore, the predetermined maximum value by which the voltage of the pacing output can be reduced by at most each day can be set such that the period during which the energy consumption of the implantable medical device is higher than necessary is limited to a few days or weeks. In that way, during the first period of operation of the implantable medical device, for example immediately after implantation, the pacing output can be set to a high level. In a further example, during a third period, a limited reduction in the voltage of the pacing output can be used. A fairly high pacing output for achieving cardiac capture can then be guaranteed, even when the patient's cardiac tissue has not yet been definitively affected by the stimulation by the pacing pulses.

In one embodiment, the predetermined maximum step down size is in the range of 0.05V to 0.2V, particularly 0.075V to 0.15V, and particularly 0.1V to 0.12V.

In one embodiment, the observation period and/or the first period is a period ranging from 7 to 50 days, in particular from 10 to 45 days, in particular from 15 to 40 days, in particular from 20 to 35 days, in particular from 25 to 30 days. In one embodiment, the first period has the same length as the observation period, i.e. the first period is equal to the observation period. In one example, the observation period extends for 30 days. The first period then extends for the last 30 days prior to the date on which the pacing output of the stimulation unit is adjusted according to the method used by the presently claimed implantable medical device.

In one embodiment, the second period of time is a period of time ranging from 2 to 14 days, in particular from 3 to 13 days, in particular from 4 to 12 days, in particular from 5 to 11 days, in particular from 6 to 10 days, in particular from 7 to 9 days. Particularly suitable second periods of time are periods of time ranging from 2 to 6 days, for example 3 days, 4 days, 5 days or 6 days.

One aspect of the present invention relates to a method for controlling the operation of an implantable medical device for stimulating the human or animal heart according to the above description, the method comprising the steps described below.

First, electrical signals of the human or animal heart are detected using a detection unit. This detection serves to detect capture thresholds during an observation period. Each capture threshold is detected in response to a sequence of pacing pulses delivered by a stimulation unit for stimulating a cardiac region of the same heart.

The detected capture threshold is stored in a memory unit of the implantable medical device.

Furthermore, the inter-threshold difference between two successive capture thresholds in each case is determined.

Then, it is determined whether the difference between the maximum determined thresholds within the observation period is equal to or greater than a predetermined limit value (first option) or is less than a predetermined limit value (second option). In the first option, the pacing output of the stimulation unit is adjusted based on the maximum capture threshold determined within the first period. In this context, the first period is equal to or less than the observation period. In the second option, the pacing output of the stimulation unit is adjusted based on the maximum capture threshold determined within the second period. In this context, the second period is less than the first period. The first period and the second period are periods that extend from the time of adjusting the pacing output of the stimulation unit to the past.

One aspect of the present invention relates to a computer program product comprising computer readable code that, when executed on a control unit, causes the control unit to perform the following steps:

First, electrical signals of the human or animal heart are detected using a detection unit. This detection serves to detect capture thresholds during an observation period. Each capture threshold is detected in response to a sequence of pacing pulses delivered by a stimulation unit for stimulating a cardiac region of the same heart.

The detected capture threshold is stored in a memory unit of the implantable medical device.

Furthermore, the inter-threshold difference between two successive capture thresholds in each case is determined.

Then, it is determined whether the difference between the maximum determined thresholds within the observation period is equal to or greater than a predetermined limit value (first option) or is less than a predetermined limit value (second option). In the first option, the pacing output of the stimulation unit is adjusted based on the maximum capture threshold determined within the first period. In this context, the first period is equal to or less than the observation period. In the second option, the pacing output of the stimulation unit is adjusted based on the maximum capture threshold determined within the second period. In this context, the second period is less than the first period. The first period and the second period are periods that extend from the time of adjusting the pacing output of the stimulation unit to the past.

One aspect of the invention relates to a medical method of treatment of a human or animal patient in need of such treatment, the treatment being performed by an implantable medical device for stimulating the human or animal heart, in particular by an implantable medical device according to the above description. Such an implantable medical device comprises a control unit, a storage unit, a stimulation unit for stimulating a cardiac area of the human or animal heart and a detection unit for detecting cardiac electrical signals of the same. The method comprises the steps described below.

First, electrical signals of the human or animal heart are detected using a detection unit. This detection serves to detect capture thresholds during an observation period. Each capture threshold is detected in response to a sequence of pacing pulses delivered by a stimulation unit for stimulating a cardiac region of the same heart.

The detected capture threshold is stored in a memory unit of the implantable medical device.

Furthermore, the inter-threshold difference between two successive capture thresholds in each case is determined.

Then, it is determined whether the difference between the maximum determined thresholds within the observation period is equal to or greater than a predetermined limit value (first option) or is less than a predetermined limit value (second option). In the first option, the pacing output of the stimulation unit is adjusted based on the maximum capture threshold determined within the first period. In this context, the first period is equal to or less than the observation period. In the second option, the pacing output of the stimulation unit is adjusted based on the maximum capture threshold determined within the second period. In this context, the second period is less than the first period. The first period and the second period are periods that extend from the time of adjusting the pacing output of the stimulation unit to the past.

Thereafter, the human or animal heart is stimulated by applying pacing pulses by the stimulation unit with the pacing output adjusted in the previous step. The pacing pulses can thus have different amplitudes depending on the previously observed variability of the capture thresholds. Typically, the pacing pulses have a higher amplitude (i.e. the stimulation unit is operated with a higher pacing output) if the variability of the detected inter-threshold difference was relatively large. In contrast, the pacing pulses have a lower amplitude (i.e. the stimulation unit is operated with a lower pacing output) if less variability was determined between the individual capture thresholds, i.e. the inter-threshold difference was relatively low.

A further aspect of the present invention is another implantable medical device for stimulating the human or animal heart, which may be combined with any of the previously described embodiments, but is claimed independently from the previously described aspects and embodiments. This further implantable medical device comprises a control unit, a memory unit, a stimulation unit for stimulating a cardiac region of the human or animal heart, and a detection unit for detecting electrical signals of the same heart.

The storage unit contains a computer readable program that, when executed on the control unit, causes the control unit to perform the steps described below.

First, the capture thresholds are detected using the detection unit during an observation period. In this context, each capture threshold is detected in response to a sequence of pacing pulses delivered by the stimulation unit.

The detected capture threshold is stored in the memory unit.

The voltage of the pacing output of the stimulation unit is lowered by at most a predefined maximum value each day. In this context, the voltage of the pacing output remains at least as high as the maximum capture threshold determined within a period equal to or less than the observation period. According to one embodiment, the voltage of the pacing output remains at least as high as the maximum capture threshold determined within a period equal to or less than the observation period with an added safety margin. In doing so, it is ensured that the applied voltage of the pacing output is always at least as high as the determined capture threshold with an added safety margin, but at the same time it is ensured that it is lowered only in small steps from the previous value. This helps to deal with sudden lowering of the capture threshold, which may only be temporary. According to one embodiment of the invention, a predefined value is defined which represents the maximum value for the variation of the pacing output, in particular for one lowering of the pacing output.

In one embodiment, the limited reduction in voltage of the pacing output is performed only for a predetermined period of time, for example, only during the third period as defined above.

In one embodiment, the predetermined maximum value is in the range of 0.05V to 0.2V, particularly 0.075V to 0.15V, and in particular 0.1V to 0.12V.

In one embodiment, the implantable medical device not only implements a limited reduction in the initial voltage of the pacing output, but also adjusts the pacing output according to the observed capture threshold variability. In this embodiment, the computer readable program causes the control unit to adjust the pacing output of the stimulation unit according to either a first option or a second option. According to the first option, if the maximum inter-determined threshold difference within the observation period is equal to or greater than a predefined limit value, the pacing output is adjusted based on the maximum capture threshold determined within the first period. In this context, the first period is equal to or shorter than the observation period. According to the second option, if the maximum inter-determined threshold difference within the observation period is smaller than a predefined limit value, the pacing output of the stimulation unit is adjusted based on the maximum capture threshold determined within the second period. In this context, the second period is shorter than the first period.

Thus, in this embodiment, the voltage of the pacing output is reduced by a predefined maximum value each day until it reaches the output of the algorithm assessing the historical capture threshold variation. This mode of operation ensures that no capture events are avoided. However, if the output of the algorithm assessing the historical capture threshold variation results in a required capture threshold that is higher than the last pacing output voltage minus the maximum value by which the pacing output voltage has been reduced at most each day, the pacing output is immediately updated to a pacing output determined based on the maximum capture threshold determined by the algorithm.

One aspect of the invention relates to a method for controlling the operation of an implantable medical device for stimulating a human or animal heart, the method comprising the steps of: a) detecting capture thresholds during an observation period using a detection unit for detecting electrical signals of the human or animal heart, each capture threshold being detected in response to at least one pacing pulse or a sequence of pacing pulses delivered by a stimulation unit for stimulating a cardiac region of the same heart; b) storing the detected capture thresholds in a memory unit of the implantable medical device; and c) reducing the voltage of the pacing output of the stimulation unit by at most a predetermined maximum value each day, such that the voltage of the pacing output remains at least as high as the maximum capture threshold determined within a period equal to or shorter than the observation period. According to one embodiment, the voltage of the pacing output remains at least as high as the maximum capture threshold determined within a period equal to or shorter than the observation period with an added safety margin.

One aspect of the invention relates to a computer program product comprising computer readable code that, when executed on a control unit, causes the control unit to perform the following steps: a) detecting capture thresholds during an observation period using a detection unit of an implantable medical device for stimulating a human or animal heart, the detection unit being configured to detect electrical signals of the human or animal heart, each capture threshold being detected in response to a pacing pulse delivered by a stimulation unit of the implantable medical device, the stimulation unit being configured to stimulate a cardiac region of the same heart; b) storing the detected capture thresholds in a storage unit of the implantable medical device; and c) reducing the voltage of the pacing output of the stimulation unit by at most a predetermined maximum value each day, the voltage of the pacing output remaining at least as high as the maximum capture threshold determined within a period equal to or less than the observation period. According to one embodiment, the voltage of the pacing output remaining at least as high as the maximum capture threshold determined within a period equal to or less than the observation period with an added safety margin.

One aspect of the invention relates to a method for treating a human or animal patient in need of such treatment with an implantable medical device for stimulating the human or animal heart, the implantable medical device comprising a control unit, a storage unit, a stimulation unit for stimulating a cardiac region of the human or animal heart, and a detection unit for detecting the same cardiac electrical signals, the method comprising the steps of: a) detecting a capture threshold during an observation period using the detection unit, each capture threshold being detected in response to a pacing pulse delivered by the stimulation unit; b) storing the detected capture threshold in the storage unit; c) reducing the voltage of the pacing output of the stimulation unit by at most a predetermined maximum value each day, the voltage of the pacing output remaining at least as high as the maximum capture threshold determined within a period equal to or shorter than the observation period with an added safety margin; and d) stimulating the human or animal heart by applying pacing pulses with the pacing output adjusted in the previous step.

All embodiments of the individual implantable medical devices described herein may be combined in any desired manner and transferred to each of the other implantable medical devices, the described methods, and the described computer program products. Furthermore, any embodiments of the described methods may be combined in any desired manner and transferred to each of the other methods, different implantable medical devices, and computer program products. Finally, any embodiments of the computer program products may be combined in any desired manner and transferred to each of the other computer program products, the described implantable medical devices, and the described methods in any combination.

Further details of aspects of the present invention will be described with reference to exemplary embodiments and the accompanying drawings.

1 is a schematic workflow of a first embodiment of a method for determining the pacing output of a stimulation unit of an implantable medical device. 1 is a schematic workflow of a second embodiment of a method for determining the pacing output of a stimulation unit of an implantable medical device.

Figure 1 shows the workflow of the method implemented by a cardiac pacemaker as an implantable medical device. First, the detection unit of the cardiac pacemaker serves to detect 110 the capture threshold during an observation period. Then, a determination 120 of the inter-threshold difference between two successive capture thresholds is performed.

Then, a determination 130 is made whether the maximum inter-threshold difference determined within the observation period is equal to, greater than or less than a preset limit value, which in the example of FIG. 1 is set to 0.4 V. If the maximum inter-threshold difference is at least 0.4 V, a selection 140 of the maximum capture threshold of the last 30 days is made. In this context, 30 days is the first period. On the other hand, if the maximum inter-threshold difference is less than 0.4 V, a selection 150 of the maximum inter-threshold difference of the last 3 days is made. In this context, 3 days is the second period. Then, an addition 160 of a safety margin to the selected maximum capture threshold is performed.

Finally, an adjustment 170 of the pacing output for pacing pulses by the stimulation unit of the implantable medical device is performed. This adjustment is based on the selected maximum capture threshold and defines the pacing output to be the sum of the selected capture threshold and a safety margin.

This method is typically applied once a day via a cardiac pacemaker.

The safety margin added to the maximum capture threshold selected in step 160 is selected to be 0.4 V if the cardiac pacemaker has not been implanted for more than a predetermined period since implantation, and is reduced to 0.3 V if the cardiac pacemaker implantation has been performed for more than a predetermined period. According to one embodiment, the predetermined period is 20 to 150 days, or 50 to 120 days, or 70 to 120 days, or 90 to 120 days, or 100 to 120 days, or 112 days.

Figure 2 shows a schematic workflow of a further method applied by another cardiac pacemaker serving as a further example of an implantable medical device.

First, a capture threshold determination 210 is performed during an observation period. This detection is performed using a detection unit of the cardiac pacemaker. Each capture threshold is determined in response to a sequence of pacing pulses delivered by a stimulation unit of the cardiac pacemaker.

The capture threshold typically serves to adjust the pacing output of a cardiac pacemaker. However, before adjusting the pacing output, a decision 220 is made regarding a reduction in the pre-applied pacing output. If the voltage U of the pre-applied pacing output reduced by 0.1 V is at least as high as the determined capture threshold CT (optionally plus a safety margin), then an adjustment 230 of the pacing output is made to the pre-applied pacing output reduced by 0.1 V.

However, if the determination 220 gives a result that the detection 210 of the capture threshold (optionally plus a safety margin) results in a capture threshold CT higher than the pre-applied pacing output voltage U reduced by 0.1 V, then an adjustment 240 of the pacing output based on the determined capture threshold is made (the safety margin is optionally taken into account and added to the detected maximum capture threshold). According to one embodiment, the pacing output is immediately increased to the output determined by the algorithm.

This method ensures that the pacing output is iteratively decreased by a maximum value, set to 0.1 V in this example, until it reaches the algorithm-determined pacing output. This method is implemented such that if the required capture threshold is unexpectedly elevated, the pacing output is automatically increased, and safe cardiac capture can always be guaranteed.

Furthermore, even if no iterative reduction of the previous pacing output is performed, this method ensures that the applied pacing output never falls below the required capture threshold.

The embodiment shown in FIG. 2 can be combined with the embodiment of FIG. 1 or can be implemented without the embodiment of FIG. 1 in a cardiac pacemaker.

Claims (3)

An implantable medical device for stimulating a human or animal heart, comprising a control unit, a memory unit, a stimulation unit for stimulating a cardiac area of the human or animal heart, and a detection unit for detecting cardiac electrical signals of the same,
When the storage unit is executed on the control unit,
a) detecting (210) capture thresholds during an observation period with the detection unit, each capture threshold being detected in response to a pacing pulse delivered by the stimulation unit;
b) storing the detected capture threshold in the storage unit;
and c) reducing each day a voltage (U) of the pacing output of the stimulation unit by at most a predetermined maximum value, wherein the voltage (U) of the pacing output remains at least as high as a maximum capture threshold determined within a period equal to or shorter than the observation period. The implantable medical device of claim 1, wherein the predetermined maximum value is in the range of 0.05 V to 0.2 V. The implantable medical device according to claim 1 or 2, characterized in that the computer readable program causes the control unit to i) adjust the pacing output of the stimulation unit (140; 170) if the maximum decision threshold difference within the observation period is equal to or greater than a predetermined limit value based on the maximum capture threshold determined within a first period, the first period being equal to or less than the observation period (140; 170), or ii) adjust the pacing output of the stimulation unit (150; 170) if the maximum decision threshold difference within the observation period is less than the predetermined limit value based on the maximum capture threshold determined within a second period, the second period being less than the first period (150; 170).